sir J. F. W. Herschel on the Art of Photography. 365 



of the first formation of an exterior crust. This permanence has 

 frequently been insisted on, and is highly important as connected 

 with the speculations of the author on the causes of that change of 

 temperature wliich has probably taken place in the higher latitudes : 

 all previous proofs of this fact having rested on the assumption of 

 the earth's entire solidity; an assumption which, whatever may be 

 the actual state of our planet, can never be admitted as applicable 

 to it at all past epochs of time, at which it may have been the habi- 

 tation of animate beings. 



The author concludes, by expressing a hope that he may be enabled 

 to prosecute the inquiry still further, and to bring before the Royal 

 Society, at a future time, the matured results of his speculations. 



March 14. — A paper was read, entitled, "An Experimental In- 

 quiry into the Formation of Alkaline and Earthy Bodies, with re- 

 ference to their presence in Plants, the Influence of Carbonic Acid 

 in their generation, and the equilibrium of this gas in the atmo- 

 sphere." By Robert Rigg, Esq. Communicated by the Rev. J. 

 B. Reade, ]M,A., F.R.S. 



The object of the author, in the present memoir, is to show that 

 the solid materials which compose the residual matter in the analy- 

 sis of vegetable substances, and which consist of alkaline and earthy 

 bodies, are actually formed during the process of fermentation, whe- 

 ther that process be excited artificially, by the addition of a small 

 quantity of yeast to fermentable mixtures, or take place naturally 

 in the course of vegetation, or of spontaneous decomposition. His 

 exj^eriments also tend to show that this formation of alkaline and 

 earthy bodies is always preceded by the absorption of carbonic acid, 

 whether that acid be naturall)^ formed or artificially supplied. He 

 finds, also, that different kinds of garden mould, some being calca- 

 reous, others siliceous, and others aluminous, exposed in retorts to 

 atmospheres consisting of a mixture of carbonic acid gas and com- 

 mon air, absorb large quantities of the former, combining with it 

 in such a manner as not to aff'ord any traces of this carbonic acid 

 being disengaged by the action of other acids. He considers the 

 result of this combination to be the formation of an alkaline bod)', 

 and also of a colouring matter. Tlais combination takes place to a 

 greater extent during the night than during the day ; and in gene- 

 ral, the absorption of carbonic acid by the soil is greatest in pro- 

 portion as it is more abundantly produced by the processes of vege- 

 tation ; and conversely, it is least at the time when plants decom- 

 pose this gas, appropriating its basis to the purposes of their own 

 system. Hence he conceives that there is established in nature a 

 remarkable compensating provision, which regulates the quantity of 

 carbonic acid in the atmosphere, and renders its proportion constant. 



A paper was also read, entitled, " Note on the Art of Photogra- 

 phy, or the a])plication of the Chemical Rays of Light to the i)ur- 

 poses of Pictorial Representation." By Sir John F. W. Herschel, 

 Bart., K.H., V.P.R.S., &c. 



The author states that his attention was first called to the subject 

 of M, Daguerrc's concealed photographic processes, by a note from 



